1. Field of the Invention
The present invention relates to a throw-away style cutting tip used for cutting a cast iron and a steel.
2. Description of Related Art
Throw-away style cutting tips have been used for cutting a cast iron and a steel. Throw-away tips that have modified rake face configurations have been known, such as those having a chip breaker formed in the rake face so as to protect the rake face from being damaged by removed metal chips, and those having a land formed near a cutting edge along the periphery of the rake face in order to prevent damage from cutting resistance or the like.
Throw-away tips having chip breakers and lands formed on both sides have such an advantage as both sides can be used in cutting operations. When such a throw-away tip has the cutting edge on one side worn out, the throw-away tip is turned over so as to carry out cutting operation using the cutting edge on the opposite side. A throw-away tip that uses the edge on either side by turning over is generally designed such that height of the land 25 is lower than a seating surface 27 (middle of the rake face) (h>0) as shown in FIG. 13, in order to prevent the cutting edge from making contact with a tool holder and being damaged (see, for example, Japanese Unexamined Patent Publication No. 8-39306).
However, according to the throw-away tip described above, height of a tip-corner 33 that has the greatest effect on attaching (seating) of the throw-away tip 21 becomes lower. Therefore, when the throw-away tip is used in a cutting operation under conditions involving severe impact, a cutting edge 24 located at the bottom surface (seating surface) of the throw-away tip 21 is lifted. As a result, seating of the throw-away tip 21 becomes insecure thus leading to vibration of the corner 33 during cutting operation. This causes the possibility of the cutting edge 24 located at the bottom surface of the throw-away tip 21 hitting the seating surface of the tool holder intermittently and resulting in breaking (breaking on the back), and/or chattering vibration of the throw-away tip which may cause chipping of the cutting edge 24 engaged in the cutting operation, during cutting.
To avoid such problems, Japanese Unexamined Patent Publication No. 11-277307 discloses a throw-away tip that has so-called full-circumference chip breaker comprising the land 25 and a central surface 27 having similar configuration to the land 25, wherein the land 25 and the central surface 27 are formed at the same height so as to secure the seating of the throw-away tip 21, prevent breaking on the back and reduce the cutting resistance.
The throw-away tip 21 of full-circumference chip breaker, however, also has such a problem that, in case the land 25 of the rake face is damaged due to chipping of the edge 24 or a crater wear during cutting operation with one side of the throw-away tip, the damaged land 25 at a corner portion 33 that has the greatest effect on seating of the throw-away tip 21 cannot provide satisfactory seating surface when the throw-away tip 21 is turned over. As a result, stability of seating is lowered while undesirable movements of the throw-away tip 21 such as lifting and chattering vibration cannot be suppressed and causing such problems as tool damage and/or rough machined surface.
There is also such a problem that, the longer the land surface on one side of the principal surface, the lower the rigidity and more susceptible to deflection. Particularly when used in a cutting operation under conditions involving severe impact, deflection of the land surface causes chattering vibration which may result in damage of the cutting edge. This problem becomes particularly conspicuous in a throw-away tip having diamond shape that has longer on one side line of the principal surface.
The above-mentioned Japanese Unexamined Patent Publication No. 11-277307 describes that cutting resistance is reduced by forming the chip breaker. However, since the chip breaker gradually warps over a wide area, chips tend to entangle when cutting a material of which chips are hard to break such as steel, thus resulting in such a problem that chips are caught between the cutting tool edge and the workpiece thus disabling stable cutting operation. Also in the case of the above-mentioned publication, since the chip breaker groove is wider and accordingly proportion of the contact surface to the entire seating surface is not sufficient, there is a weakness in securely fastening the throw-away tip.
Moreover, simply decreasing the width of the chip breaker groove reduces the effect of warping the chips and breaking them. When the chip breaker is made narrower and deeper, there arises the possibility that chip flow of discharging the chips from the cutting zone is compromised, resulting in such a problem that chips are caught around the cutting tool edge or the chip breaker groove.